Impulse stimulating apparatus



Feh 50 J. A. mm; Em, 2,498,882?

IIIPUISE STIHULATING APPARATUS Filed June 20, 1946 llllllll 1 v llllll 1' I llllllllllllllll 'vvvvvv' Patented Feb. 28, 1950 IMPULSE STIMULATING APPARATUS James A. Fizzell and James G. Golseth, Chicago,

Ill., assignors, by mesne assignments, to Research Corporation, New York, N. Y., a corporation of New York Application June 20, 1946, Serial No. 678,150

9 Claims. 1

This invention relates to an impulse stimulating apparatus and more particularly to an electrical impulse stimulating apparatus for the electrodiagnosis of peripheral nerve injuries.

Peripheral nerve injuries may be diagnosed by electrically stimulating muscle through the skin and observing the character of the muscle reaction in response to the stimulation. Diagnosis of the character of peripheral nerve injuries; i. e., to determine whether a nerve is divided or contused, by clinical examination not utilizing electrical stimulation, is often dimcult if not impossible. While contused nerves usually recover spontaneously, those that are divided require operative repair and the sooner this is done the better are the results obtained. Therefore, the use of an electrical impulse stimulating apparatus is of great aid in diagnosing peripheral nerve injuries.

' As the character of the muscle reaction to the electrical impulse stimulation furnishes a guide as to the type of nerve injury involved and because this muscle reaction Will usually be controlled by the amount and duration of electrical current used as a stimulus, it is necessary to have an apparatus that will deliver the proper type of electrical current to the patient in precise controllable amounts. The operator must know definitely what the apparatus is delivering so that any variations in results can be attributed to the patients condition and not to improper performance of the apparatus. Only then can these variations be properly interpreted in the light of established standards and only then can comparisons be made of results obtained by using different machines. Therefore, the apparatus must be a precise one and particularly is this so if satisfactory results are to be obtained in clinical research of peripheral nerve injuries.

Our apparatus meets these standards. It will deliver monophasic (direct) current, which has been found to be preferable to multiphasic (alternating) current for electrodiagnosis of peripheral nerve. injuries, in precise controllable amounts. The electric current is delivered in pulses controllable in duration and controllable in time interval between pulses so that, if desired, a practically continuous current can be obtained. The pulses are square wave pulses so that, when the electrical current is applied to the patient, it is applied practically instantaneously at full pulse amplitude value.

We also provide switching means for reversing polarity of the electric current delivered to the patient, since current polarity is a factor in electrodiagnosis of peripheral nerve injuries, and for isolating the patient from the electric current when the value of current delivered to the patient is being measured, thereby avoiding patient discomfort.

In order that the character of the load; i. e., intermittent electric current application to the patient and variations in the electrical resistance of different patients, will not adversely affect the source of direct current, which may possess poor voltage regulation and hence affect the character of the electric current delivered to the patient, we provide means for obtaining a substantially constant electric current drain on the source or direct current during operation of our apparatus.

We are aware that apparatus has been proposed for use in electrodiagnosis which produces pulses of direct current and which includes an arrangement intended to effect a constant electric current drain on the source of direct current while the apparatus is in operation. However, we have found this prior art apparatus to lack suilicient precision for satisfactory usage in electrodiagnosis of peripheral nerve injuries by percutaneous stimulation. There is insuflicient control of pulse duration and pulse frequency and the pulses obtained with this prior art apparatus are not square waves. The result is that the overall precision of the prior art apparatus is not suitable for accurate electrodiagnosis and, in particular, is not suitable for comparing examinations made with different machines or for clinical research. We overcome the defects of this prior art apparatus by a novel combination of elements described hereafter.

Accordingly, an object of the present invention is to provide a new and improved apparatus for electrodiagnosis having means for generating pulses of direct current, means for delivering these pulses to a patient, and means for maintaining a substantially constant current drain on the source of direct current during operation of the apparatus.

Other objectsof the present invention are to provide such an apparatus, wherein square wave pulses of direct current are produced with delicate control of the pulse current strength, the pulse duration and the interval between pulses, wherein the polarity of the current delivered to the patient can be reversed and, when the cur rent is being measured, the patient can be isolated from the electrical circuit, and wherein the apparatus is portable and easy to set up and operate.

These and other objects of our invention will become apparent from the following detailed description taken-inconjunction with the accompanying drawings, inwhich Fig. 1 is a diagram of the electrical circuit of our apparatus with the polarity control switch shown in neutral position;

Fig. 2 is a diagram of the polarity switch posi tion for making the exploring electrode the anode;

Fig. 3 is a diagram of the polarity switch position for making the exploring electrode the cathode, and

Fig. 4 is a frontal view of the apparatus housing, with the cover removed, showing the control panel and the members contained thereon and also showing the electrodes through which current is delivered to a patient.

Referring to Fig. 1, which illustrates an embodiment of our invention, the major parts of our invention include an output circuit designated at l and including electrodes l3 and M for delivering current to a load l5, such as a patient, a milliammeter l6 for measuring the intensity of the current delivered to the load, a pentode tube I! for controlling the flow of current delivered to the load, and a switch assembly [8 for interconnecting the electrodes I3 and I4, the milliammeter l6 and the pentode I I, across the source of direct current; a compensating circuit H for maintaining a substantially constant current drain on the source of direct current and ineluding a pentode IS, a voltage divider 20 and connections 2| and 22 interconnecting control elements of pentodes l1 and I9 with voltage divider 20 in a manner such that the total current drawn by the output circuit l0 and the compensating circuit ll remains substantially constant during operation of our apparatus; and a multivibrator circuit l2 for generating pulses of direct current to be delivered to the load IS.

The electrodes 13 and I4 are of a type which can be conveniently applied to portions of the human body being examined and are illustrated in greater detail in Fig. 4. Electrode I3 is preferably made in ball form so that it can be pressed against the skin and the electrode is extended into an insulated handle portion 23 so that the electrode can be grasped by an operator and manipulated at will. This electrode is theexploring electrode and, in practice, is moved over the surface of the skin to determine the correct point for application of electric current. Electrode I4 is shown as constituting a substantially fiat plate which can be clamped against a portion of the body and held stationary during application of electric current to the patient.

' Elastic clamping members can be used to clamp the electrode I4 to the patient and extensions 24 serve as guides for preventing slippage of the electrode [4 from the elastic retaining means. Electrode I3 is connected through lead 25 to stationary contacts 28 and 21 of switch assembly 58. Electrode I4 is connected through lead 28 to stationary contacts 29 and 30 of switch assembly l8.

Direct current is delivered to the electrodes l3 and M from the positive side 3| of the D. C. source. The current passes through milliammeter l6 before reaching the electrodes. After passing through the electrodes, the current passes through pentode l! to the negative side 32 of the D. C. source. ,The milliammeter i6 is connected to the positive side 3! of the D. C. source by lead 33 and is connected to a movable contact member 34 of switch assembly l8 by lead 35. The plate 33 of pentode i1 is connected to movable contact 31 and stationary contact 38 of switch assembly l8 by lead 39. Lead Zl connects the screen grid 40 of pentode I! to the voltage divider 20 at point 4| and lead 42 connects the control grid 43 of pentode I! to the output circuit 44 of multi-vibrator circuit 12 at points 45 .and 46. Cathode 41 of pentode I1 is connected through resistance 48 to the negative side 32 of the D. C. source.

In the compensating circuit H the plate 49 is connected to the positive side 3| of the D. C. source through lead 50. The screen grid 5| of pentode I9 is connected to a resistance 52, which is across the D. C. source, by lead 53, as is shown in Fig. l. The control grid 54 of pentode i9 is connected to the voltage divider 20 at point 55 by lead 22. Cathode 56 of pentode i9 is connected, through resistance 48, to the negative side 32 of the D. C. source.

Multi-vibrator circuit l2 includes pentodes 51 and 58, capacitors 59 and 60, and resistances GI, 62, 63 and 64 connected in conventional electroncoupled multi-vibrator fashion, as is illustrated in Fig. 1, to produce square wave pulses of direct current. In the connection shown in Fig. 1, the screen grids 65 and 66 of pentodes 51 and 58, are used as plates for the performance of the switching function. A portion of the electron stream in pentode 58 reaches the plate proper 61 because this plate is made positive by its connection through resistance 68 to the positive side 3| of the D. C. source and this portion of the electron stream furnishes the voltage pulse in resistor 68 which is transmitted through lead 69, to the output circuit 44 of the multi-vibrator circuit l2. Thus the load is coupled to the oscillatory circuit through the electron stream in the tubes themselves. As will be evident to those skilled in the art, this manner of coupling achieves square wave pulses in the output and prevents changes in the load from affecting the frequency of oscillation. Resistances 63 and 64 are adjustable for changing the time constants of the circuits of the respective tubes 57 and 58. Control of the interval between pulses is obtained by adjusting resistance 63 and control of the duration of the pulses is obtained by adjusting resistance 64. Control of the pulse amplitude or current strength of the output pulses is obtained by adjustable resistance 10.

For portability, the electrical elements are housed in a casing ll of size and shape as illustrated in Fig. 4. This casing is provided with a grip member 12 for carrying the casing and has a hinged cover, shown as removed, which covers the control panel 13. Mounted on the control panel are adjustable dials 14, I5 and 16. Dial l4 adjusts resistance 63 and thus controls the interval between pulses, dial l5 adjusts resistance 54 and thus controls the duration of the pulses, and dial l6 adjusts resistance 10 and thus controls the pulse current strength. Milliammeter I6 is mounted on control panel 13 and a switch handle ll is also contained thereon for controlling the switch assembly l8. Leads 25 and 28 project from the control panel 13 through opening- 18.

Switch assembly 58 is a three-position switch, which is illustrated as being in the middle, or neutral position in Fig. l. The arrows 19 indicate that the movable contacts can be moved either to the left or to the right and these positions are indicated in Figs. 2 and 3 respectively. When the movable contacts are in the position shown in Fig. 1, electrodes I3 and I4 are eliminated from the output circuit. When the movable contacts are in,the -position shown in Fig. 2, electrode I3, the exploring electrode, is the positive electrode, or anode, and when the movable contacts are in the position shown in Fig. 3, electrode I3 is the negative electrode. Thus, the direction of current passing through load I5 can be reversed by moving the movable contacts of switch assembly I8 to either extreme position. Movement of these contacts to the left, middle, or right hand positions can be eifected by moving switch handle TI to the left, middle, or right hand position.

The operation of our apparatus is as follows: When the switch 80 is closed, positive direct current flows to the output circuit I 0, the compensating circuit II, and the multi-vibrator circuit I2. In the switch position illustrated in Fig. 1, this current flows through milliammeter I6, through lead 35, through switch contacts 34 and 3|, through connecting lead 82, through switch contacts 83 and 38, and through lead 39 to the plate 35 of pentode II. Conduction of current through the pentode I! to the negative side 32 of the D. C. source is controlled by control grid 43 which, in turn, is connected through lead 42 to the output circuit 44 of multi-vibrator circuit I2. It is a well known characteristic of electron discharge units such as, for example, the pentode I1, that operation of such a unit on the flat portion of its characteristic curve, that is, the curve illustrating the relationship between plate-voltage and platecurrent, eliminates the variations in current caused by varying resistances. Pentode I! is operated on the saturated portion of its plate voltage-plate current characteristic curve with the result that changes in plate circuit resistance, as will occur when load I5 is connected into the circuit, have little eifect on the value of plate current. Pentode I! is also biased so that when control grid 43 is driven in a positive direction by the action of multi-vibrator circuit I2 the pentode will conduct current to the negative side 32 of the D. C. source. Thus, it will be seen that for the switch position illustrated in Fig. 1, electrodes I3 and I4, and hence the load I5, are eliminated from the current path so that current readings can be taken without discomfort to the patient. Furthermore, resistance 84 is included in the multivibrator circuit I2 and this resistance, acting in conjunction with resistance 64, increases the time constant of resistance 64 and condenser III (which time constant controls the duration of the pulses applied to the subject), to such a value that a practically continuous current is passed by pentode II thereby enabling the operator to read milliammeter IS without having the milliammeter needle fluctuating. v

While current has been passing through the output circuit I0, additional current has also been passing through voltage divider 20 and pentode that the total current drain remains substantially I9. When pentode I1 is non-conducting, voltage divider 20 and pentode I9 draw a substantially constant current. However, when pentode I1 is conducting, the screen grid 40 of pentode I'I draws current from voltage divider 20 through lead 2| with the result that the potential of point 55 on voltage divider 2D is reduced. Since control grid 54 of pentode I9 is connected by lead 22 to point 55, the control grid 54 is simultaneously made more negative, thereby reducing the current passed by pentode I9. Thus, as pentode I1 conducts, pentode I9 conducts a lesser amount of current and the circuit constants are chosen so constant whether pentode I1 is conducting or non-conducting.

When the switch contacts are in the position shown in Fig. 2, current passes from the positive side 3I of the D. C. source, through milliammeter I6, through lead 35, through switch contacts 34 and 25, through lead 25 to electrode I3, through the load I5, to electrode I4, from electrode I4 through lead 28, from lead 28 through switch contacts 30 and 31 to lead 33 and from there to plate 36 of pentode II, whence pentode I! conducts the current then passing through that tube to the negative side 32 of the D. C. source. Thus, in this switch position electrode I3 is the positive electrode. The compensating action of the compensating circuit II and the control eiIected by multi-vibrator circuit I2 are the same as was explained for the switch connection illustrated in Fig. 1, with the following exception.

When the movable switch contacts are moved either to left or right position, resistance 34 is shorted out by the action of movable contact and stationary contacts 83 and 81. This'restores control of the pulse duration to adjustable resistance 64, which can be varied as desired to achieve different pulse durations.

When the movable switch contacts are in the position illustrated in Fig. 3, current flows from the positive side 3i of the D. C. source, through milliammeter I5, through lead 35, through switch contacts 34 and BI, through lead 82, through switch contacts 83 and 29, through lead 28 to electrode I4, throughthe load I5 to electrode I3, from electrode i3 through lead 25 to switch contact 21, through switch contact 27 and switch contact 37 to lead 39 and from lead 39 to the plate 36 of pentode I7. Current then passes through pentode I! to the negative side 32 of the D. C. source. Thus, in this switch position the electrode I4 is the positive electrode and electrode I3 is the negative electrode, or cathode. Operation of the compensating circuit II and the multivibrator circuit I2 is the same as was explained for the switch position illustrated in Fig. 1, and the resistance 84 is likewise shorted out by the action of switch contacts 85 and 8! to restore control of the resistance 64.

Thus, the operator may apply direct current pulses of controllable duration and interval therebetween and of controllable strength to a load, such as a patient, and he can vary the polarity of the current passing through the load at will. The exploring electrode I 3, which he will.

normally hold in his hand, can be made either an anode or cathode; i. e., a positive or negative electrode. When he desires to read the value of current that was delivered to the patient he merely has to throw the switch to neutral position and the patient is isolated from the circuit. Furthermore, the pulse duration is automatically thrown to practically continuous current so that he can read current value as a steady value and this value will be the same as the value of current delivered to the patient because the electronic tube controlling this current delivery is substantially unaifected by variations in its plate resistance. The power supply is unaffected by current drain because the current drawn by the output circuit is compensated by an additional circuit so that a substantially constant current drain is maintained on the current source.

It will be seen that we have provided a portable impulse stimulating apparatus of suflicient prepulse duration to the adjustable susceptible to other uses.

cision for use in accurate electrodiagnosis of peripheral nerve injuries preferably by percutaneous stimulation of muscle.

While we have referred to the use of our impulse stimulating apparatus for electrodiagnosis, it is to be realized that such an apparatus is For example, it will find other electromedical uses, such as for electrotherapy and, in particular, the stimulating of paralyzed muscles resulting from peripheral nerve injuries and other neurological disorders. In short, such an apparatus can be used whenever it is desired to apply electrical current to a load, such as a patient, in the manner heretofore described.

Likewise, while we have described a particular embodiment of our invention, it is to be understood that we do not wish to be restricted thereto and that we intend to cover all modifications thereof which would be apparent to one skilled in the art and which come within the spirit and scope of our invention, as set forth in the appended claims.

We claim:

1. An apparatusfor delivering pulses of direct current to a load and for maintaining a substantially constant current drain on the source of direct current while the apparatus is in operation comprising an output circuit having a pair of electrodesadapted to be connected to the load, a current intensity indicating device and a space discharge device, all adapted to be connected in series across the direct current source by a switch having three positions, in two positions of which the electrodes are in the output circuit but have difierent polarities and in the third position of which the electrodes are out of the output circuit and the current intensity indicating device and the space discharge device are connected in series across the direct current source, a compensating circuit having a second space discharge device connected, through a resistance, across the direct current source, said second space discharge device being biased to draw normally a constant current, and a connection between the first named space dischargejevice and the second space discharge device for lowering the current drawn by the second space discharge device, when the first named space discharge device is conducting, in an amount suficient to keep the total current drain on the source of direct current substantially constant, a multi-vibrator circuit for generating pulses of direct current, said multi-vibrator circuit having means to vary the pulse duration, the interval between pulses and the pulse current strength, and a connection between the output circuit of said multi-vibrator circuit and a control member of the first named space discharge device whereby the current delivered to the load is controlled by the action of the multi-vibrator circuit.

2. An impulse stimulating apparatus for electromedical use or the like comprising an output circuit having a pair of electrodes adapted to be connected to a load, a current intensity indicating device, and a multi-element space discharge device, all adapted to be connected in series across a source of direct current by a multiple position switch having positions for reversing the direction of current to the load and for isolating the load from the output circuit, means for maintaining a substantially constant current drain on the direct current source during operation of the apparatus, an electron-coupled multivibrator for generating substantially square wave pulses of direct current, said multi-vibrator including means for varying the pulse duration, interval between pulses and pulse current strength and a connection between the output circuit of said multi-vibrator and a control member of said multl-element space discharge device whereby operation of saidspace discharge device is controlled by said multi-vibrator.

3. An apparatus for electromedical use or the like comprising a source of direct current, an output circuit having a load circuit, a milliammeter and a space discharge device, all adapted to be connected in series across the direct current source by a multiple position switch, a compensating circuit having a second space discharge device connected, through a resistance, across the direct current source, said second space discharge device being biased to draw normally a substantially constant current, and means to decrease the current drawn by said second space discharge device when said first named space discharge device conducts by an amount sufiicient to maintain the current drain on the direct current source substantially constant during operation of the apparatus, a multi-vibrator connected across the direct current source and means for impressing the output of said multi-vibrator on a control element of said first named space discharge device, said first named space discharge device being biased to respond to impulses produced by said multi-vibrator.

4. An apparatus for electromedical use or the like comprising a source of direct current, means for producing pulses of direct current, means for delivering said pulses to a load, said last named means including a pentode tube, a second pentode tube connected, through a resistance, across the direct current source, said second named pentode being biased to draw normally a substantially constant current, a voltage divider connected across the direct current source, a connection between a control element of said firstnamedpentode and said voltage divider, a connection between a control element of said second named pentode and said voltage divider, said last named connection being at a less positive potential point on said voltage divider than said first named connection, whereby when current passes from the said first-named pentode through a portion of said voltage divider and produces a voltage drop across said portion, the potential of said second named connection, and hence the potential of the control member of the second named pentode, is further decreased to decrease the current drawn by the second named pentode.

5. An apparatus for electromedical use or the like comprising a source of direct current, an output circuit having a pair of electrodes adapted to be connected to a patient, a milliammeter, and a pentode, all adapted to be connected in series across the direct current source by a three position switch having two positions for reversing the polarity of current delivered to the patient and a third position for isolating the patient from the output circuit while the milliammeter is being read, a compensating circuit having a second pentode connected, through a resistance, across the direct current source, a voltage divider connected across said source, and means interconnecting said voltage divider with both of said pentodes to maintain the current drain on the direct current source substantially constant during operation or the apparatus, an electron-coupled multi-vibrator connected across the direct current source for producing pulses of direct current, said multi-vibrator including means for varying the duration of said pulses,

of said first named penin the potential of said multi-vibrator output circuit are impressed upon said control grid, said first named pentode being biased to be responsive to said potential variations.

6. An impulse stimulating apparatus for electromedical use or the like, comprising an output circuit having electrodes adapted to be connected to a load, a current intensity indicating device, and a multi-element space discharge device, all adapted to be connected in series across a source of direct current by a multiple position switch having at least one position in which the load is isolated from the output circuit, a multi-vibrator for generating pulses of direct current, said multi-vibrator including a resistance for controlling pulse duration and also including an output circuit, a connection between said output circuit and a control member of said multi-element space discharge device, said control element being biased to be operatively responsive to the output of said multi-vibrator circuit to control current flow through said multi-element space discharge device, and a shunt circuit through said multiple position switch for shunting out the resistance in said multi-vibrator when the load is isolated from the first named output circuit, whereby a practically continuous current is produced by said multi-vibrator and is impressed on said multi-element space discharge device control member to cause a practically continuous current to pass through the current intensity indicating device to facilitate reading the value of current.

7. An apparatus for delivering pulses of unidirectional current to a load comprising a source of unidirectional current, a first space discharge device, a multi-vibrator, a compensating circuit current drained by said second space discharge device when the first space discharge device conducts by an amount sumcient to maintain the means to measure the intensity of the current being delivered to the load, means to isolate the load from the pulse-delivering means while the value of the current delivered to the load is measured, and variable resistance means connecting said last-named means to the pulse-producing means to cause said pulse-producing means to produce long briefly interrupted pulses while the current is being measured.

9. An apparatus for delivering pulses of unidirectional current to a load comprising a source of electrical potential, means connected across said source for setting up pulses of unidirectional current, a first thermionic valve connected across said source in series with the load, means for feeding said pulses to a control element of said valve, a second thermionic valve also connected across said source and normally biased to draw a given amount of current when the first valve is non-conducting, and circuit means interconnecting said valves for reducing current flow through said second valve by an amount equal to the current flow through the first valve as occasioned by the action of said pulses on said control element of said first valve, whereby the total current drawn on said source remains constant irrespective of varying load.

JAMES A. FIZZEIL. JAMES G. GOLSETH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,092,496 Branson Sept. 7, 1937 2,185,367 Blumlein Jan. 2, 1940 2,189,317 Koch Feb. 6, 1940 2,403,984 Koenig, Jr., et a1. July 16, 1946 2,414,479 Miller Jan. 21, 1947 2,428,058 Wise Sept. 30, 1947 FOREIGN PATENTS Number Country Date 387,518 Great Britain Feb. 9, 1933 OTHER REFERENCES Pages 448 to 454, inclusive, of Tousey, Medical Electricity and Roentgen Rays, published in 1910 by W. B. Saunders 00., Philadelphia, Pa. 

